pulse-width modulation

In this paper, a step-up converter with very high voltage gain and low input current ripple for photovoltaic systems is presented. One of the main features of the converter is not using coupled- inductors and increasing gain by using switched-capacitors, so the volume and weight of the converter has been greatly reduced. The auxiliary circuit has provided zero voltage switching conditions for the main and auxiliary switches, and due to the low number of elements, the efficiency of the converter has been significantly improved. The input current ripple of the converter is very low, which makes it easy to track the maximum power point from the photovoltaic cells. Due to the increase in gain and decrease in voltage stress on the switches, it is possible to use switches with lower RDS(on), and conduction losses are subsequently reduced. Also, due to the complementary function of the switches, the design of the control circuit is simple and the control of the converter remains as PWM. The converter is simulated in PSPICE software with a power of 110 W and an output of 330 V, and finally a prototype is made of it, and the laboratory results confirm the simulation results.

In this paper, a high step-up converter with a high voltage gain and low voltage stress on the switches is presented, which enables zero-current soft switching for both switches. The designed auxiliary circuit not only ensures soft switching conditions for the converter components but also transfers the snubber energy to the output. This circuit includes only one snubber capacitor, one auxiliary diode, and one coupled inductor. The proposed converter was simulated in Pspice software with a power of 110 W and an output of 340 V, and the obtained results are in good agreement with theoretical analyses. Additionally, a laboratory prototype of the converter was constructed, showing a 5.5% improvement in efficiency compared to its hard-switching counterpart.

Multi-level inverters (MLIs) have now become an essential component for medium and high power applications with medium voltage levels. Low switches multi-level inverters are very popular due to their high efficiency, low cost, and easy control for output with higher levels. In this paper, a new multi-level inverter structure based on a switched DC voltage source is proposed by reducing the number of switches for single-phase applications. The proposed structure can be used in grid-connected applications, such as grid connections for renewable energy sources. The proposed structure is developed with a higher number of levels at the output using a smaller number of devices. The proposed topology can also be used in symmetric and asymmetric configurations. Two switching methods including pulse width modulation (PWM) switching and ladder switching based on selective harmonic elimination (SHE) have been used to generate the output voltage. Comparative studies with multilevel inverters were presented recently to show the advantage of the proposed structure in terms of reducing the number of devices. Simulation and experimental results are presented to confirm the performance of the proposed topology. In addition, the performance of the proposed multilevel structure for energy transfer from renewable sources to the low-power grid has also been investigated.

The commutation torque ripple adversely affects the performance of the six-phase inverter of the BLDC motor with trapezoidal back EMF and creates vibration and noise for industrial applications. In this paper, the motor model is obtained in non-commutation times and during the commutation period, and according to that, a suitable method to reduce the torque ripple, by equalizing the slope of the current disconnected from the motor and the slope of the current connected to the motor during commutation, is presented. At low speeds, torque ripple is reduced using predictive pulse width modulation technique. With this method, the duty cycle of the switch involved in the commutation is predicted and applied to the switch during the commutation intervals. At high speeds, this reduction is done using quasi z-source converter and selector circuit. The quasi z-source converter and the selector circuit increase the input voltage of the inverter during commutation intervals and increase its value to four times the back EMF voltage of the motor, thus reducing the torque ripple at high speeds. The theoretical and analytical results are verified using the simulations performed in the PLECS software.

In this paper a quasi z-source DC-DC converter is proposed that provides soft switching condition for all semiconductor devices with only two resonant paths without the use of any auxiliary circuitry, as well as any auxiliary switch. Based on the proposed structure, only one switch is used in the circuit, which greatly simplifies the performance of this converter in comparison with the similar structures. Also, the non-isolated structure and the lack of use of transformers and even coupled inductors to increase the voltage gain have led to the simplicity and high efficiency of the proposed converter. The converter efficiency is 95.8% at full load range. The control technique of the converter is simple and the pulse width modulation (PWM) is used to trigger the switch. Due to use of high switching frequency, the total size and volume of the converter especially for passive elements in its structure has decreased. The converter is completely analyzed and simulated in the software environment. Also, a 40-360V 50W laboratory prototype operating at 100 kHz is implemented. The experimental results confirm the simulation results and theoretical analysis.